Looking at the date of the posts; the problem is probably already solved but nevertheless.
I ran in the same problem with xfce4 and vlc; trying to find some solution to it by googling etc...
Couldn't find anything in bugs. At last i tried nvlc in a terminal and this worked. So nothing seemed to be wrong with vlc.
Then I remembered something about rvlc, qvlc somewhere mentioned. Could my problem have something to do with
trying to start vlc from trying to start it from the menu; and something there isn't configured wright. freedesktop-stuff perhaps.
But wait; what if the gui wich vlc wants to use when started from the start-menu; simply isn't there. I've installed vlc; saw it in
the start-menu and presumed everything was well. xfce4 is based on gtk+; does vlc have a gtk-gui?
vlc comes with all kind of interfaces but I didn't remember a gtk one, and after some searching I couldn't find one.
There is however qvlc, probably a qt4-gui; and my qt4 USE-flag isn't set in make.conf, and i would like to keep it that way.
So lets set qt4 only for the package vlc; I use
euse -E qt4 -p media-video/vlc
You can get euse by emerge gentoolkit.
Then re-emerge vlc; and now it works out of the start-menu without freezing the xfce4, it tried before to load a gui wich wasn't
there.
Hope this helps anyone running in the same problem